1. Field of the Invention
This invention relates to pigment dispersants which have good usability and are particularly effective in rendering pigments non-floculating and non-crystallizing in nature.
2. Description of the Prior Art
In general useful pigments which exhibit bright color and high color strength in ordinary various coating compositions consist of fine particles. However, it is known that when fine pigment particles are attempted to be dispersed on non-aqueous vehicles such as offset inks, gravure inks and paints, it is difficult to obtain stable dispersions, with various problems being involved in manufacturing operations. Such problems give important influences on the value of final products.
For instance, dispersions comprising pigments in the form of fine particles have often high viscosity, which makes it difficult to withdraw the dispersion product from a dispersion machine and transport it. In a worse case, the dispersion may gel during storage and cannot be used. Where different types of pigments are used in combination, lack of color uniformity and/or a considerable lowering of color strength may be experienced in pigment compositions due to the separation or flocculation by agglomeration of the pigments and also due to the settlement thereof. In addition, the surface of the film obgtained from such pigment composition may involve some drawbacks such as lowering of gloss, leveling failure, and the like.
Although not directly related to the dispersion of pigment, there is known a phenomenon inherent to some organic pigments in which the crystalline state of the pigment varies. More particularly, when placed in non-aqueous vehicles such as of offset inks, gravure inks and paints, crystal particles of a pigment which are unstable from the standpoint of energy are varied in size and shape, and are converted to a more stable state. As a consequence, the composition suffers a considerable change of hue, a reduction of color strength, and formation of coarse particles, thus lowering the commercial value to a substantial extent.